Body: Small Breast
Calm, Fast Learner, No sense of Self, Strong Willed, Emotionless Expression, Protected (by Asakura Ryoko), Not quite Human
An alien created by the Integrated Data Sentient Entity, She was sent to North High to watch over Haruhi Suzumiya, who has the ability to create new data, something the Integrated Data Sentient Entity lacks, and desires. Due their nature as data life forms they possess the ability to manipulate data, allowing them to alter reality.
However, due to "errors" (which Kyon classifies as "emotions") Yuki steals some of Haruhi's powers to create an alternate universe in which Haruhi, Itsuki, Yuki, and Mikuru are normal humans, Haruhi and Itsuki do not attend North High, Ryoko is a student, and there is no SOS Brigade. Due to this incident, the Integrated Data Sentient Entity threatens to delete Yuki. Instead, a compromise is made. A limiter would be placed on her abilities, and she will not be deleted.
Due to this restriction, she is unable to prevent the plot of the rouge esper group transplanting Haruhi's powers to Sasaki, and is captured along with most of the SOS Brigade and sold into slavery.